Recent studies have established the presence of an olfactory input to the mediodorsal nuclear complex of the thalamus, an area which has been known primarily as the thalamic dependency of orbitofrontal cortex. This new evidence for an olfactory thalamocortical relay brings olfaction into line with other sensory systems and provides fresh information on the largely unknown functions of MD and orbitofrontal cortex. The objective of the proposed research on rabbit, opossum and monkey is a combined electrophysiological-anatomical determination of the sources of input to MD and of the cortical and subcortical output of MD.